1. Field of the Invention
The present invention relates to a method and associated apparatus for increasing the over cladding rate in perform production while maintaining the integrity of the glass quality of the cladding.
2. Discussion of Related Art
Due to the market pressure to decrease the price of optical fibers, there is a continuous demand to increase the overall productivity of the fabrication process. One of the first steps in the process of manufacturing an optical fiber is the plasma process. This process involves making more than 90% of the preform glass by fusing quartz sand onto the primary preform as a cladding with the aid of a hot plasma fireball.
There are two important parameters associated with this process. The first is the deposition speed (grams/min.) Of the glass and the second is the quality of the deposited glass. For a particular process, these two parameters are antagonistic to each other. Specifically, as the deposition speed increases, the glass quality is degraded.
Both of these parameters are affected by the usable power available to generate the plasma fireball. The higher the power, the greater the deposition speed and the better the glass quality. However, the conventional plasma setup has limited power capability. This limitation is not due to the output of the generator, but to the thermal resistance of the plasma torch. When the power in the plasma torch reaches a given value, the plasma torch cannot sustain the required temperature and its lifetime is shortened. It is estimated that the plasma torch only uses approximately 2/3 of the output capacity of the generator.
Conventional processes only use a single plasma torch such as is disclosed in U.S. Pat. No. 4,221,825. Thus, the full capacity of the generator is not realized and the deposition speed and quality of glass are limited.